Electric arc process and apparatus



Jan. 27, 1959 R. R. LOBOSCO ET AL 2,371,336

7 ELECTRIC ARC PROCESS AND APPARATUS O 3&3

.326 dd 5% m Filed Nov. 28, 1956 ATTORNEY 319 l LO+Q- HHHLL M B oEk m V 3&3 W W copi Durham 1 comfiizxz! L United States Patent ELECTRIC ARC PRO'CE5S AND APPARATUS Roscoe R. Lobosco, Fanwood, Joseph E. Messina, Roselle, and Glenn W. ()yler, Springfield, N. J., assignors to Union Carbide Corporation, a corporation of New York Application November 28, 1956, Serial No. 624,845

4 Claims. (Cl. 219-44) This invention relates to electric arcs and more particularly to the starting of high-pressure arcs in media of relatively high ionization potential.

According to the invention there is provided an improved process of starting a main high-pressure arc in a stream of gas having a relatively high ionization potential, which involves first energizing a pilot high-pressure arc in a stream of gas having a relatively low ionization potential at a relatively low arc current, starting a relatively high current main arc current in such ionized gas stream, and using the relatively high current supplying such main arc to feed relatively high ionization potential gas to such stream,

The invention is very suitable for starting shaped or constricted arcs of the type disclosed by Gage in his application, Serial No. 524,353, filed July 26, 1955; especially when used for the purpose of cutting metals as disclosed by Oylcr et al. in their application, Serial No. 540,951, filed October 17, 1955; both of which applications are owned by the assignee of the present application.

Apparatuswise, the invention is concerned with a nontransferred arc torch that is first supplied with argon gas, for example, that has a relatively low ionization potential through a gas feed line. A direct current circuit of relatively low current value (about amperes) is connected to energize a pilot are between the end of the primary electrode of such torch and a laterally positioned pilot electrode in the resulting stream of argon gas that flows about such primary electrode and is discharged from the torch as an ionized argon gas pilot efliuenta Such pilot eiiluent of ionized argon is used to conduct the much higher current of a main arc in a direct current circuit that includes said primary electrode and a work electrode such as an electrically conductive piece of metal. A relay, responsive to such higher current, opens a valve in a hydrogen feed line that leads to such are torch, feeding hydrogen to such stream as long as the main arc is energized.

In cutting with the shaped-arc torch of Gage, resistance of the gas gap between the electrode and the workpiece is so great that the main arc cannot transfer across such gap without assistance. The main or cutting arc must, therefore, be struck with the aid of a helper or pilot arc. A difiiculty was encountered in starting caused by the use of hydrogen, a relatively high resistance gas, as a constituent of the cutting gas and by the high velocity of the issuing cutting jet of ionized gas, electrical resistance being a function of gas velocity.

When a conventional power supply is used, such as a motor-generator with an open-circuit potential of 100 volts, it is impossible to strike a pilot are between electrode and torch cup with the normal argon-hydrogen cutting gas mixture. It was found, however, that the pilot arc could be struck and stabilized in an atmosphere of pure argon and then hydrogen gas could be added coincidentally with the initiation of the cutting arc.

Therefore, a novel control circuit is provided that is "ice capable of delivering a flow of pure argon for the striking and maintaining of the pilot arc and, when the cutting arc is struck, automatically adding hydrogen to the argon to give the proper cutting gas mixture.

When the operator lowers his helmet to begin cutting there is usually not enough light for him to see his workpiece. If he should start his cut in the wrong place he would damage the workpiece. The pilot arc efiluent avoids such difliculty by providing the necessary light by which the operator can see the workpiece and start the cut at the proper place.

After a main line switch has been turned on, the control circuit is ready for operation. Pressing of a torch switch energizes a starting relay. Such switch must remain closed until cutting action begins. A step-down transformer is used to supply a safe low voltage across the torch switch. This is a feature designed to protect the operator. The starting relay in turn energizes in the following sequence:

(1) An argon gas solenoid valve coil, causing a predetermined flow of argon gas to pass through the cutting torch.

(2) A high-frequency generator, the high-frequency output of which ionizes a path between the electrode and the torch cup.

(3) A main contactor, if sufficient cooling water is flowing to close the contacts of the flow switch. This in turn completes a D. C. circuit from the negative terminal of a D. C. power supply to the primary electrode in the torch. Direct current fiows from the power supply through the ionized path btween the electrode and torch cup and back to the positive terminal of the power supply through a set of resistors.

These steps take place automatically and they allow the striking of the pilot arc. The voltage across the resistors operates the pilot arc relay which de-energizes the high-frequency relay by opening the normally closed contacts. An adjustable resistor is connected in series with the pilot arc relay to protect the latter from overvoltage before the main arc is established.

If the torch switch is released at such time, the starting relay will be de-energized, the argon solenoid valve will close and the main contactor will open. Thus, the pilot arc will be extinguished. This is a fail safe feature designed to protect the operator and the torch.

However, assuming that the pilot arc has been established when the nozzle is brought close to the work, the

main arc will transfer to the work. The cutting current then energizes the current relay which, in turn, energizes the hydrogen solenoid valve. This causes a predetermined fiow of hydrogen to pass through a common hose into the torch and provides a gaseous mixture for the cutting jet. The current relay also allows the by-passing of the starting relay and this provides a holding circuit so that the operator can release the torch switch.

The cut is then made. At the end of the cut, the are loses its ground and is extinguished. This deenergizes the argon and hydrogen solenoid valves and opens the main contactor. The control set-up is then ready for the next operation.

In the drawing,

The single figure is a circuit diagram illustrating the invention.

It is believed that such circuit diagram will be understood by those skilled in the art from the following description of the operating sequence thereof.

To begin cutting, .it will be assumed that the v. A. C. supply has been connected to the control. The primary winding 6 of transformer 8 has been energized. The torch push button 9 is depressed completing the circuit from the 25.2 volt secondary winding 7 of transformer 8 through the torch push button 9, through start relay to secondary winding 7. Start relay 10 operates, closing contacts 11 of start relay 10.

Then:

(1) A circuit is completed from one side of 115 v. A. C. main supply through contacts 11 of relay Ill, through argon solenoid valve 1 to 115 v. A. C. supply line. Argon solenoid valve 1 opens and argon flows through flowmeter 2 to torch 27.

(2) A second circuit is completed from one side of 115 v. A. C. main supply through contacts 11 of relay it) through water solenoid valve 3 to 115 v. A. C. supply. Water solenoid valve opens and water flows through Water cooled torch cup 23. However, in practice, as a safety procedure to protect the torch, this circuit is generally kept closed before, during, and after the cutting operation.

(3) A third circuit is completed from one side of 115 v. A. C. main supply through contacts 11 of start relay 1%? through operating coil of main contactor relay coil 12 to 115 v. A. C. supply line. Contacts 13 of relay 12 close and open circuit voltage of D. C. power supply 14 is applied to input connections of high-frequency generator l5.

(4) Afourth circuit is completed from one side of 115 v. A. C. main supply through contacts 11 of relay 10 through closed contacts 17 of pilot arc relay 16 to 115 v. A. C. supply terminals 26 of high-frequency generator 15 to the other side of the 115 v. A. C. main supply.

The high-frequency generator 15 supplies a high-frequency voltage from the negative output terminal to electrode 24 of torch 27 through relay 20, from the cup 23 through resistor 19 to input positive terminal of high-frequency generator 15. The high-frequency voltage causes a spark to jump from the electrode 24 to torch cup 23 of torch 27 and completes the following circuit.

From the negative output terminal of high-frequency generator 15 to electrode 24 via a high-frequency spark to cup 23 of torch 27 through resistor 19 to positive input terminal of high-frequency generator 15. This circuit completes and establishes the pilot arc.

The pilot arc completes the following circuit.

From negative output terminal of high-frequency generator 15 to electrode 24 of torch 27 through the pilot arc to cup 23 through voltage dropping resistor 18, through pilot arc relay to to positive input terminal of bi h-frequency generator 15. The pilot are relay 16 operates and its contacts 17 open and deenergize the high-frequency 115 volt supply circuit.

The torch cup 23 is lowered to approximately from the work 25 and the pilot arc establishes the main cutting are from negative output terminal of highfrequency generator through relay through electrode 24 of torch through cutting arc to work 25 to the positive output terminal of high-frequency generator.

Current relay 20 is energized by the main cutting arc from negative output terminal of high-frequency generator through current relay 2% through electrode 24 of torch through cutting arc to work 25 to positive output terminal of high-frequency generator.

The contacts 21 of current relay 29 close and complete the following circuit.

rom one side of 115 v. A. C. supply through contacts 21 of relay 2% through hydrogen solenoid valve 4 to other side of 115 v. A. C. supply. The hydrogen solenoid valve 4 opens and hydrogen flows from hydrogen supply through hydrogen valve 4 through flowmeter 5 to torch 27 where it is fed into the cutting are.

The contacts 22 of current relay 20 close and complete the following holding circuits.

(1) From one side of 115 v. A. C. supply through contacts 22 of relay 20 through main contactor relay coil 12 to the other side of 115 v.

(2) Through water solenoid valve 3.

(3) Through argon solenoid valve 1.

Once the holding circuits have been completed and the cutting arc has been established, the torch push button 9 may be released. The torch 27 is moved along the work 25 at a uniform speed and the cut is made.

The methods of stopping the cutting are are as follows:

(1) Moving the torch off the edge of the workpiece at completion of the cut.

(2) Lifting the torch from the work above normal cutting arc length.

(3) Depressing the emergency stop push button (not shown on diagram). I

The circuit operation for above methods 1 an 2 are as follows:

The cutting arc is extinguished by exceeding the normal cutting arc length. The are power circuit is opened between the electrode 24- and workpiece 25. The current relay 20 deenergizes and opens contacts 21 and 22. Open contacts 21 and 22 deenergize the contactor relay 12, and the argon, hydrogen, and water valves.

What is claimed is:

1. Process of starting a main highpressure arc in a stream of gas having a predetermined ionization potential, which comprises starting a pilot high-pressure arc of predetermined arc current in a stream composed of gas having an ionization potential that is lower than that of the gas of the stream of such main arc, starting a main high-pressure arc with such pilot arc in such lower ionization potential gas stream at an arc current that is higher than that of such pilot arc, and changing the composition of such stream with such higher are current to gas having an ionization potential that is higher than that of the gas of the stream of such pilot are.

2. Process of starting a shaped arc in a stream of gas having a relatively high ionization potential, which involves first energizing a pilot high-pressure are in a stream of gas having a relatively low ionization potential at a relatively low arc current, starting a relatively high current main arc in such ionized gas stream, and using the relatively high current supplying such main arc to feed relatively high ionization potential gas to such stream at a substantially greater feed rate than that of such pilot arc gas.

3. Process of starting a main high-pressure arc in a stream of gas containing hydrogen having a relatively high ionization potential, which involves first energizing a pilot high-pressure arc in a stream of argon gas having a relatively low ionization potential at a relatively low arc current, starting relatively high current main arc current in such ionized argon gas stream, and using the relatively high current supplying such main arc to add hydrogen gas to such stream of argon.

4. Are torch apparatus comprising an arc torch including a primary electrode surrounded by a gas cup having a discharge orlice axially aligned with said primary electrode, means for feeding one gas to the annular space between said cup and electrode, which gas flows about the end of the electrode and out of such orifice, a pilot arc circuit including said electrode and a pilot electrode carried by said cup for carrying a pilot arc in the gas stream discharged by such cup, a main arc circuit including said primary electrode and a Work electrode for energizing a main arc therebetween in such ionized pilot arc gas stream, acurrent relay in said main arc circuit, and means including a shut-off valve operated by said relay for feeding another gas to said are torch for discharge from such orifice with such stream in response to the operation of such main arc.

References Cited in the file of this patent UNITED STATES PATENTS Cochrell et al; Sept. 13, 

